The forecast says "Early afternoon thunderstorms are expected to become slow-moving and merge together to produce some larger and more persistent areas of thunderstorms.

"This will lead to torrential rain with 30-40mm of rain possible in an hour and a good chance of as much as 60-80mm rain in 2-3 hours in some places. As well as this, frequent lightning and large hail are possible."

The Met Office has issued advice for the severe weather, which can be viewed here.

Network Rail is to introduce a blanket speed restriction across many parts of the Great Western network following an amber weather warning for heavy rain showers and thunder storms.

The speed restrictions are being put in place as a matter of precautionary safety for passengers and train staff, between 4pm through to 6am Friday, June 1 and which will significantly impact GWR’s train service.

Passengers are advised to travel as early as possible, and to check before they travel and, where possible, consider changing travel plans, as the situation is likely to deteriorate quickly.

Ticket restrictions have been lifted allowing those with off peak tickets to travel on peak time services, and allowing customers who choose not to travel today to be able to do so tomorrow.

Those who do need to travel are advised to expect late notice cancellations and delays to services where they can be provided.

The warning comes in light of the emergency weather warning issued by the Met Office for the South West, GWR expects services towards Bristol, South Wales, Exeter, the north and south Cotswolds to be affected.